Stereotactic surgical techniques allow physiological exploration and/or destruction of deep cerebral or spinal cord structures which are invisible from the surface, but which location can be determined by a knowledge of their coordinates in space relative to known anatomical and topographical landmarks. The use of stereotaxis in neurosurgical techniques seeks to avoid open operative approaches to these areas with a minimum of disturbance to surrounding structures. The technique generally involves the placement of fine electrodes or probes in strategic "target areas" which may comprise specific functional anatomical sites or morphological lesions or abnormalities. One of the major difficulties of stereotactic surgery is graphic conceptualization of the location of surgical probes inserted into deep brain structures. Not only is the probe out of the surgeon's sight, but it is tilted, rotated, and extended in many different directions, which circumstance makes it almost impossible for the surgeon to maintain a mental picture of the location of the probe in the brain core. The surgeon must imagine the location of the probe while taking into account the forward and lateral angles of the probe, the distance of the probe from the target, the direction that the electrode extends from the probe, and many other angular variables. Furthermore, the coordinate system of the stereotactic frame seldom corresponds to the "brain coordinate system," causing greater margin of error and difficulty in placement of the probe. Stereotactic surgery, therefore, is essentially a "blind" surgical procedure with many complex geometric variables. Any system which will enhance the surgeon's conceptualization of the procedure will greatly enhance its efficacy.
The introduction of stereotaxis to the armamentarium of human neurosurgical technique has been an important addition. This is evident by its use in the treatment of many neurological disorders. This technique has expanded from its earlier use, primarily in the treatment of dyskinesias and pain syndromes, to include the treatment of seizure disorders, aneurysms, brain tumors and many other neuropathological conditions. In recent years there has been a significant increase in the number and use of stereotactic surgical techniques. This has been brought about by the development of new imaging technologies, for example, computerized axial tomography (CT), nuclear magnetic resonance (NMR) scanning, various radioisotope scanning techniques, and digital subtraction angiography (DSA). These imaging techniques allow the surgeon to "see" certain brain structures and to use these imaging technologies to aid in planning stereotactic surgical procedures.
Computed tomography (CT) is well established as a valuable diagnostic and investigative imaging device and has revolutionized the evaluation and treatment of neurological conditions. Applications and use of CT technology with stereotactic and functional neurosurgery are increasing. Advancing computer technology has been the basis upon which CT scanning technology has developed; this same technology is supporting the development of the newer digital subtraction angiographic (DSA), various radioisotope scanning, and nuclear magnetic resonance (NMR) imaging systems.
The increased resolution afforded by such scanning systems allows direct identification of brain structures that could only be inferred from conventional roentgenological techniques. Stereotactic surgery, being primarily a procedure performed without the aid of direct visualization, is dependent on sophisticated imaging techniques for its accurate execution. Therefore, it necessarily follows that as computer and imaging technology improve, so do the possibilities of stereotactic surgery. The present invention is primarily concerned with the use of computer-graphics techniques and scanning techniques for generating various composite images to better aid the stereotactic surgeon in localizing structures, such as subcortical structures, lesions, or abnormalities.
Non-computer systems have been developed in the art for stereotactic surgery. These systems use spatial coordinate determinations based upon the use of special plastic type grids and measurement devices. These systems are based upon hand plotting and calculation of coordinate positions. Some disadvantages to such systems are that they are cumbersome, slow, relatively inaccurate, have very limited use, and are specific for only one type of scanning device and manufacturer.
Software routines on hand-held calculators, e.g., HP41C, Sharp, and Epson HX20, have also been developed in the art for use with stereotactic surgery. Calculations are done by the use of a calculator instead of a grid and specific measuring instruments. Parameters for coordinate determination are entered into the calculator's functions by the use of similar grids. Some disadvantages of these systems are the same as the non-computer spatial coordinate systems described above.
Some parent scanning devices, e.g., CT scanner, NMR scanner, etc., contain resident software systems. Rule grids are placed over the image in the scanner via a software graphics package of limited capabilities. Accuracy is limited, since measurements are done in "screen coordinates" and therefore the systems do not take into consideration various rotations of the patient's head or other body parts in the scanning device. These are purely systems for calculating coordinates and have no operative simulating capabilities. CT scanners and NMR scanners also have some image manipulation routines which consist of various means of ramping image grey scales for contrasting; however, they contain none of the other features of the present invention, such as brain anatomical mapping techniques, electrophysiological mapping, extensive image manipulation, image comparison, 3-D simulations, etc. By design, each of these systems is limited to use in a specific scanner and its use must be sanctioned by the scanner designer, such as shown in "The Role of Computed Tomographic and Digital Radiographic Techniques in Stereotactic Procedures for Electrode Implantation and Mapping, and Lesion Localization," by T. M. Peters, et al., Appl. Neurophysiol., Vol. 46, pp. 200-205 (1983). Image sources from several different scanners cannot be compared. Too, all functions must be carried out in each specific scanner device which monopolizes the scanner's use. Another disadvantage is that improvements or modifications to these systems cannot be made as scanner manufacturers tend to resist or disallow the addition of non-proprietary software and/or hardware to their scanning systems since they are potentially at risk of incurring additional liability should the software and/or hardware not function as intended.
Other prior art systems utilize IBM PC type computers, including clones, and other desktop type personal computer versions. In some of these versions, either a camera input interface is used to acquire scan images from an X-ray plate type hard copy into the computer's video display, or magnetic transport media is utilized, most notably magnetic computer tapes. One disadvantage of these systems is that these existing interface designs rely upon the digitized images acquired through a camera input. The camera is mounted over an X-ray type hard copy image of the scanner image section to obtain an image. These systems can be inherently inaccurate because they use various kinds of camera lens designs and different image aberrations result from different lens designs. These include warping and distortion of the image due to chromatic aberration, spherical aberration, coma, astigmatism, and various other aberrations which result from deviation of refracted or reflected light rays from a single focus, or their convergence to different foci, due to the spherical shape of the lens or mirror. It is difficult to adjust or compensate for these problems. Another disadvantage is that existing interface designs rely upon the transportation of digital data from the original scanning source via use of magnetic transport media, most commonly tapes or floppy disks. Such transport media are not standardized and different scanner manufacturers use different digital formatting methods and formats in their systems. Marketing and servicing any system utilizing magnetic transport media to obtain images is extremely difficult due to tremendous and variable software overhead and frequently incompatible hardware designs of magnetic tape and disk drives. Such systems are heavily dependent upon acquiring proprietary information from the scanning device manufacturers with regards to how their image is digitally formatted. The digital format of images varies considerably among scanner types, scanner manufacturers, and even scanner versions from a single manufacturer. Transportation and use of such systems has to be custom designed for each scanner at different institutions and frequently has to be changed, depending upon the particular image formatting version used at an institutional scanning site. Software overhead is therefore extensive and almost impossible to service. Furthermore, these systems are difficult to use since there is also considerable incompatibility among tape manufacturers, tape reading methods, and hardware. Such systems can be quite confusing for the user. Furthermore, such systems have limited use since they do not have the computer processing power which is currently available in faster outputting systems, and have no specific means of comparing images from different scanning sources. Some of these systems, however, have some rudimentary image manipulation and simulation capabilities.
Devices utilizing large computer systems which use magnetic transport media and multiple image displays also exist. There is currently one system apparently available for use which is resident in a large scanner computer which uses a tape interface for acquiring images from several sources and displays the images on a plurality of monitors. One disadvantage of such device, as previously discussed, concerns the inherent difficulties associated with magnetic transport media. In addition, difficulties encountered with resident software systems, also previously discussed, are present in this large computer using system. This system is additionally particularly large and costly and requires a computer engineer to competently operate the system, which is beyond the ability of the average neurosurgeon to operate by himself. Significantly, separate images from separate sources cannot be compared one to another or overlayed in the system. And, because of the system's very large size, it has to be housed in a separate operative suite which adds to its expense. A prior device designed by Patrick Kelly, et al., manufactured by Stereotactic Medical Systems, Inc., is such a system as described above.
The images acquired by these various prior art scanning techniques are not standardized in a common format and no method for comparing and using images from various scanners has been developed. The method and apparatus of the present invention have solved this problem, as well as other problems discussed above.
Another prior art imaging system, developed by Tyrone L. Hardy, M.D., and others (Thompson, C. J., Hardy, T. L., and Bertrand, G.; "A System for Anatomical and Functional Mapping of the Human Thalamus," Comput. Biomed. Res., Vol. 19, pp. 9-24, 1977) was designed to run on a Digital Equipment Corporation PDP-12 computer with software written in assembly-level and Fortran IV languages. This system was very large and could not be taken into an operating room. The graphics display terminal, which could be taken separately into the operating room, had to be interfaced with the computer by long coaxial linkages. Its operation was cumbersome but necessary, given the hardware constraints inherent in the computer design. Stereotactic brain maps of the diencephalon were utilized in this system. These stereotactic brain maps were the architectonics by R. Hassler ("Anatomy of the Thalamus;" Introduction to Stereotaxy with an Atlas of the Human Brain, Vol 1; G. Schaltenbrand and P. Bailey, eds. Stuttgart: Thieme, 1959, pp. 230-290) and Van Buren and Borke (Van Buren, J. M., and Borke, R. C.: "Variations and Connections of the Human Thalamus" (Springer, N.Y., 1972)), which were digitized for use in the computer. Software routines for modifying the computer displays of the brain maps corrected deficiencies in anatomical sectioning (the horizontal sections vary 8 degrees from the intercommissural plane) and variations in the sizes of the atlas maps (the frontal maps were considerably smaller than the horizontal maps). The coordinate system for the digitized atlas map sections were based, as those of the anatomical atlas maps, on a brain coordinate system constructed about the third ventricular core; that is, an intercommissural line bisected by a midcommissural line and a horizontal line representing the basal plane of the brain. This system was later extensively modified to operate in a much smaller portable computer system by Tyrone L. Hardy and Jay Koch (T. L. Hardy and J. Koch, "CASS: A Program for Computer Assisted Stereotaxic Surgery," Proceedings of the 5th Annual Symposium on Computer Application in Medical Care; Washington, D.C., 1981, pp. 1116-1126), which describes a system which ran on a smaller, more portable DEC PDP-11 MINC computer system with a Tektronix graphics terminal. This system was designed to work with older X-ray imaging technology and not with CT scans, NMR scans or PET or DSA. The system drew map images, simulated probe trajectories and printed electrophysiological data on the display terminal according to various parameters which were typed into certain program requests.
Brain stem and cerebellar maps from the newer Schaltenbrand and Wahren atlas (G. Shaltenbrand and W. Wahren, Atlas for Stereotaxy of the Human Brain (2d Ed.); Stuttgart: Thieme, 1977) afforded an opportunity to expand the computer mapping capabilities to include rhombencephalic structures. Incorporating these maps into this system required the development of a coordinate system that would allow the simultaneous display of diencephalic architectonics and the remaining brain stem and cerebellum. Allowance was also required for variations in the angle of the junction of the diencephalon with the lower brain stem. See Hardy, T. L., Koch, J., "Computer-assisted Stereotactic Surgery," Appl. Neurophysiol. Vol. 45, pp. 396-398, 1982, which describes a software modification to the above-noted system described in the 1981 paper to allow a similar use of brain stem maps and describes the development of a brain stem coordinate system. Both coordinate systems could be moved independently of each other; the size of the brain maps, including the brain-stem length, could be readily varied to match the patient's anatomical dimensions as determined from contrast ventriculograms. This was accomplished by developing a method of intersecting an upper (diencephalic) coordinate system constructed about the third ventricular core, with a lower coordinate system constructed about the fourth ventricle. For example, the angle of intersection will be closer to 90 degrees in a patient with a brachiocephalic brain in which brain-stem angulation is perpendicularly oriented. Adjustments for difference in brain-stem sizes were achieved by a software subroutine that could be prompted to expand or contract the digitized maps. As with the above-noted system described in the 1981 paper, this system was not designed to work with newer imaging technology. After the development of high-resolution, color-graphics raster display monitors that could interface with small computer systems it became possible to improve this system. The computer system was later modified so that it could use such a monitor to display CT images as well as benefit from the addition of color graphics. The result was a portable system which could store, manipulate, and selectively display CT images in the operating room independent of the CT scanner. The previously digitized atlas maps also could be superimposed on CT sections of the diencephalon. This method of graphic operative simulation served as a guide for using CT data in performing functional neurosurgery. However, this system had to be programmed separately for each type of scanner. "Computer Graphics with Computerized Tomography for Functional Neurosurgery, (T. L. Hardy, J. Koch, and A. Lassiter, Appl. Neurophysiol. Vol. 46, pp. 217-226 (1983)), describes a prototype system which could be used with CT imaging technology. This system could simulate probe trajectories but could not determine coordinates. Such parameters had to be entered by typed entry into the computer's program. The system was capable of pseudocolor, but no other image manipulation routines were possible. CT image display was limited to four bits of image capabilities which gave a gray scale capability of 2.sup.4 (16 levels). This system was fraught with difficulties and the hardware design was subsequently abandoned. Some of these difficulties were also due to the CPM based operating system which was slow, cumbersome and extremely difficult to use as a developmental platform. Hardy, T. L., Lassiter, A., and Koch, J., "A Portable Computerized Tomographic Method for Tumor Biopsy", Acta. Neurochir. [Suppl.], (Wien), p. 444, 1983, describes the above-noted system as a laboratory model for simulating tumor biopsy.